Special JSON binding in WinJS ListView - json

Question

I have problems binding this JSON to my list view.
http://pubapi.cryptsy.com/api.php?method=marketdatav2
No data is displayed.
Data.js
(function () {
"use strict";
var _list;
WinJS.xhr({ url: 'http://pubapi.cryptsy.com/api.php?method=marketdatav2' }).then(
function (response) {
var json = JSON.parse(response.responseText);
_list = new WinJS.Binding.List(json.return.markets);
},
function (error) {
//handle error
}
);
var publicMembers =
{
itemList: _list
};
WinJS.Namespace.define("DataExample", publicMembers);
})();
HTML:
<section aria-label="Main content" role="main">
<div id="listItemTemplate" data-win-control="WinJS.Binding.Template">
<div class="listItem">
<div class="listItemTemplate-Detail">
<h4 data-win-bind="innerText: label"></h4>
</div>
</div>
</div>
<div id="listView" data-win-control="WinJS.UI.ListView" data-win-options="{itemDataSource : DataExample.itemList, itemTemplate: select('#listItemTemplate'), layout: {type: WinJS.UI.GridLayout}}"></div>
</section>
I feel that the API is not that well formed.
Isnt this part a bit odd?
"markets":{"ADT/XPM":{...}...}

Answer 1

There are three things going on in your code here.
First, a ListView must be bound to a WinJS.Binding.List's dataSource property, not the List directly. So in your HTML you can use itemDataSource: DataExample.itemList.dataSource, or you can make your DataExample.itemList dereference the dataSource at that level.
Second, you're also running into the issue that the declarative binding of itemDataSource in data-win-options is happening well before DataExample.itemList is even populated. At the point that the ListView gets instantiated, _list and therefore itemList will be undefined. This causes a problem with trying to dereference .dataSource.
The way around this is to make sure that DataExample.itemList is initialized with at least an empty instance of WinJS.Binding.List on startup. So putting this and the first bit together, we have this:
var _list = new WinJS.Binding.List();
var publicMembers =
{
itemList: _list.dataSource
};
With this, you can later replace _list with a different List instance, and the ListView will refresh itself.
This brings us to the third issue, populating the List with your HTTP response data. The WinJS.Binding.List takes an array in its constructor, not an object. You're passing the parsed JSON object straight from the HTTP request, which won't work.
Now if you have a WinJS.Binding.List instance already in _list as before, then you can just walk the object and add items directly to the List as follows:
var jm = json.return.markets;
for (var i in jm) {
_list.push(jm[i]);
}
Alternately, you could populate a separate array and then create a new List from that. In this case, however, you'll need to assign that new List.dataSource to the ListView in code:
var jm = json.return.markets;
var markets = [];
for (var i in jm) {
markets.push(jm[i]);
}
_list = new WinJS.Binding.List(markets);
var listview = document.getElementById("listView").winControl;
listview.itemDataSource = _list.dataSource;
Both ways will work (I tested them). Although the first solution is simpler and shorter, you'll need to make sure to clear out the List if you make another HTTP request and repopulate from that. With the second solution you just create a new List with each request and hand that to the ListView, which might work better depending on your particular needs.
Note also that in the second solution you can remove the itemDataSource option from the HTML altogether, and also eliminate the DataExample namespace and its variables because you'll assign the data source in code each time. Then you can also keep _list entirely local to the HTTP request.
Hope that helps. If you want to know more about ListView intricacies, see Chapter 7 of my free ebook from MSPress, Programming Windows Store Apps with HTML, CSS, and JavaScript, Second Edition.